Imagine an angry face. What is its gender? A team led by D. Vaughan Becker asked this question to introductory psychology students and found that over three-fourths of the responses were "male."

There was no difference in the response based the respondent's gender. Both men and women are much more likely to think of a male "angry" face than a female one.

When asked to picture a happy face instead of an angry face, the results would switched almost as dramatically in the opposite direction: Most people say happy faces are female, although in this case, the effect is entirely due to male respondents. Women's responses are evenly divided male-female.

But the researchers weren't just interested in imagined faces. What they really wanted to know is if there's a gender bias in recognizing facial expressions. Are we more likely to perceive a male face as angry and a female face as happy? Are we quicker and better at recognizing angry faces in men compared to women? If we are, does this mean we're sexist?

Thirty-eight volunteers sat at computer monitors, which showed pictures of men and women with either angry or happy faces. The task was to indicate, as quickly as possible, whether the faces were happy or angry. Here are the results:

They were significantly more accurate identifying happy female faces compared to happy male faces. Though the difference here looks small, they were also significantly more accurate identifying angry male faces compared to angry female faces. Reaction times followed a similar pattern -- faster identifying angry males and happy females.

Next they repeated the same experiment in reverse. Instead of asking whether the faces were angry or happy, they asked whether they were male or female. Here are the results:

Once again, respondents were significantly more accurate judging happy female faces and angry male faces, and again, response times backed this up.

Are we really biased to see anger in male faces and happiness in female faces? Or do neutral male faces just look angrier than neutral female faces? The prototypical angry expression involves a furrowed brow, compressed mouth, and flared nostrils and "flashing eyes." Maybe men's typically larger brow and thinner lips compared to women just look a little angrier. Becker's team took gender neutral faces from a computer rendering program, then adjusted the parameters of the program to make each face look slightly more masculine or feminine. They showed these faces to volunteers, asking them to rate either which face was angrier or which face looked more masculine.

Even though the faces all have neutral expressions, the more masculine faces were uniformly rated as "angrier."

Taking this a step further, the researchers next took identical gender-neutral computer-rendered faces and attached them to male or female bodies. Viewers were told that the faces had been modified to appear slightly angry or slightly happy, and asked to rate each face for its perceived level of happiness versus anger.

This time, the faces on male bodies were rated as significantly less angry than the faces on female bodies.

So, far from being biased to perceive males as angry and women as happy, we appear to respond honestly to the facial expressions -- if there's any bias at all, it's in the opposite direction, to see "women" as angrier than they really are. Male faces in their neutral state simply appear angrier than female faces.

Why is a male face more like an "angry" face? The researchers say an angry face is one that we may want to avoid because of danger to ourselves. Men are physically larger and therefore more dangerous on average than women, so it makes sense that we associate the typical male face with "anger."